1. Field of the Invention
This invention resides broadly in the field of electronic musical instruments, and is particularly adaptable for use in instruments employing a digital selection system for calling forth desired tones and voices from those available to be produced by the instrument. The principles of the present invention are applicable to any electronic musical instrument in which musical sounds are generated in response to the actuation of key switches regardless of whether those switches are actuated directly, i.e., by the musician's fingers, or indirectly, by the plucking of strings. The term key is used in a generic sense, to include depressible levers, actuable on-off switches, touch or proximity responsive devices, closable apertures and so forth. The present invention relates to the attack and decay characteristic of a musical note played on an electronic musical instrument. More particularly, the present invention relates to the delay of the attack and decay functions as normally generated in an electronic musical instrument.
2. Description of the Prior Art
Heretofore, delaying the attack or decay period required the use of elements such as analog or digital shift registers or random access memories. Conventional delay elements such as these can be used to create delayed audio signals by either delaying the keying information or by delaying the waveform information in digital form, or after conversion, in analog form. Delaying the digital keying information requires delay elements clocked by a constant clocking frequency determined by the digital instrument design. Under these conditions the amount of delay is solely determined by the size and quantity of delay elements used. Adjustments in delay time cannot be continuously adjustable as in the present invention but must be adjusted in increments determined by the particular delay elements used. Delaying the digital waveform information just prior to a digital to analog conversion must be accomplished in a manner similar to delayed keying and thus provides no advantage in controlling the delay time. Continuously adjustable delay times may be obtained by delaying the audio information after conversion either by digital techniques employing further analog to digital and digital to analog conversion or by analog bucket brigade delay elements. However, delaying in this manner has disadvantages not found in the present invention. Although continuously adjustable by adjusting the propagating clock frequency, this method is considerably more complex and costly in terms of hardware and, in addition, results in an audio output signal of reduced quality. This reduced quality comes in part from the fact that the audio information must be sampled at a rate determined by the propagating clock and thus is bandwidth limited. The bandwidth, as well as the desired delaying effect, is proportional to sampling frequency, and thus as the delay time is lengthened, the bandwidth is reduced. Additional deterioration in audio quality can come from analog to digital and digital to analog converters if the delay is implemented with digital delay elements. In accordance with the present invention, digital logic is used to create a second attack or decay period for each respective note. Additionally, digital logic is provided so as to prevent any audio effect of the first attack or decay period. A significant advantage of the present invention is the elimination of common delay elements and the continuously adjustable delay time available to the player without audio degradation.